1. Field of the Invention
The present invention relates to a brake hydraulic pressure generating apparatus for increasing a brake pedal treading force during vehicle braking period.
2. Description of the Related Art
Typically, in a brake hydraulic pressure control apparatus for a vehicle, hydraulic pressures in two braking systems are controlled by two pistons. The hydraulic pressure chambers whose pressures are controlled by those two pistons are connected to wheel cylinders by fluid passages. The pistons are connected to the brake pedal through a vacuum booster as a toggle joint by making use of a negative pressure of the engine.
With such a configuration, when the brake pedal is operated, a force several times larger than the treading force of the brake pedal is generated in the vacuum booster. The pistons are operated by that force. The hydraulic pressures generated in the chambers of the master cylinder are transferred to wheel cylinders and the pressures in the wheel cylinders rise thereby applying a braking force to the wheels.
The vacuum booster provided in the foregoing structure is expensive and large. In use, then, the vacuum booster occupies a relatively large area within the limited space provided for the engine. This is particularly true in smaller, low grade vehicles. In addition, the use of a vacuum booster leads to an increase the weight and cost of the engine as well as temperature rise.
Furthermore, only one power source system based on the negative pressure of the engine is used for the toggle joint because of cost and space limitations. Thus the amplifying ratio of the device is very large. If a problem occurs in the negative pressure source system when the vehicle is being braked, the braking force will be reduced. To compensate for this reduction in braking force, a remarkable increase in the pedal stroke is required. When this happens, the driver of the vehicle may mistakenly believe that no braking force is being applied. Such a situation is very dangerous.